A gold plating film has excellent electric characteristics, corrosion resistance, solderability and the like. Due to these properties, a gold plating film is being frequently used in production of electronic members, such as a circuit board. A gold plating film is also being applied to an ornamental use due to the peculiar luster and color tone thereof.
As a gold plating bath, a cyanide bath having a cyanide compound added thereto for retaining gold ions stably in the bath has been used over the years. However, a cyanide bath is not only necessarily handled and stored with extreme attention due to the toxicity thereof, but also may not be used for plating a circuit board having fine resist pattern since the bath damages the resist.
Under the circumstances, various non-cyanide plating baths have been proposed. For example, JP-A-2006-111960 describes a non-cyanide displacement plating bath having thiouracil, aminoethanethiol, methylthiourea, aminomercaptotriazole, dihydroxymercaptopyrimidine or mercaptonicotinic acid for retaining gold ions stably.
JP-A-2000-26977 describes a noble metal electroless plating bath having as a reducing agent mercaptoacetic acid, 2-mercaptopropionic acid, 2-aminoethanethiol, 2-mercaptoethanol, glucose-cysteine, 1-thioglycerol, sodium mercaptopropanesulfonate, N-acetylmethionine, thiosalicylic acid, 2-thiazoline-2-thiol, 2,5-dimercapto-1,3,4-thiadiazole, 2-benzothiazolethiol or 2-benzimidazolethiol.
However, a more stable non-cyanide gold plating bath and a method for producing the non-cyanide gold plating bath have been demanded.